Shortly before sundown on the 29th of Adar, G-d commanded Moses regarding the mitzvah of sanctifying the crescent new moon and establishing a lunar calendar. This is the first mitzvah the Jews were given as a nation.
Moses had difficulty envisaging the moon's appearance at the exact moment of its monthly rebirth. After the sun set, G-d showed Moses the crescent new moon of the new month of Nissan, showing him the precise dimensions of the moon at the moment the new month is to be consecrated.
For the generations that followed, each new month was ushered in when two witnesses testified before the Sanhedrin (rabbinic supreme court) that they had seen the molad, the new moon. In the 4th century CE, Hillel II foresaw that the Jews would no longer be able to follow a Sanhedrin-based calendar. So Hillel and his rabbinical court established the perpetual calendar which is followed today -- until Moshiach will come and reestablish the Sanhedrin.
Links::
Lunar Time
Rosh Chodesh
The Molad
A few months after its creation, Napoleon's "Sanhedrin" (rabbinical supreme court) was dissolved. The Sanhedrin was created to approve certain religious regulations requested by the French "Assembly of Notables." The regulations were designed to blur the distinction between Jews and non-Jews.
The rulings of this pseudo-Sanhedrin were never adopted by Jewish communities.
Link:: Napoleon Bonoparte
On Yom Kippur, the souls return to connect to their origin, carrying with them the divine sparks from all they've done in this world.
Their return rises like an aroma of burning incense through the atmosphere, and through endless strata of spiritual realms, until it reaches a place beyond higher and lower. It reaches the essence of G-d.
And there it becomes the essence of pure and ultimate bliss.
On Sukkot, that divine, supernal delight reappears in our world, much as a cloud condenses from the vapor rising from the sea.
And it manifests as the branches and leaves covering our Sukkah.
So that within the Sukkah, we are embraced by G-d’s delight in us, and we rejoice.